Cutting Elements with Ridged and Inclined Cutting Face

ABSTRACT

A drill bit for cutting formation comprises a bit body, a plurality of cutters, and a plurality of blades with pockets to accommodate the cutters, respectively. Each of the plurality of cutters has a substrate, an ultra-hard layer, an inclined surface on the top of the ultra-hard layer, wherein the inclined surface slants downward from a cutting edge to a trailing edge. The cutter can improve cutting efficiency and service life.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication No. 63/030,725, filed May 27, 2020; which is incorporated byreference herein in its entirety.

FIELD

This disclosure generally relates to drill bits in oil and gas industry.The disclosure specifically relates to the cutting elements in field ofthe drill bits for petroleum exploration and drilling operation.

BACKGROUND

When drilling a borehole in the earth, such as for the recovery ofhydrocarbons or for other applications, it is a conventional practice toconnect a drill bit on the lower end of a drill string. The bit isrotated by rotating the drill string at the surface or by the actuationof downhole motors or turbines, or by both methods. The drill bit isrotated and advanced into a subterranean formation. As the drill bitrotates, cutters or abrasive structures cut, crush, shear, and/or abradeaway formation material to form a borehole. A bit generally includes abit body made from steel or matrix metal. The bit body has blades orsimilar structures to which are attached a plurality of cutting elementsin a selected arrangement. The way in which the blades are structured,and the way in which the cutting elements are arranged on the bladesdepend on, among other factors, the type of earth formations to bedrilled with the particular bit and the structure of a drilling assemblyto which the drill bit is attached.

Referring to FIG. 1, a conventional bit adapted for drilling throughformations of rock to form a borehole is shown. The bit includes a drillbit body 3 and a plurality of blades 4 and a connection or pin 32 forconnecting the bit to a drill string (not shown) which is employed torotate the bit around a longitudinal bit axis 6 to drill the borehole.The blades 4 are separated by channels or gaps that enable drillingfluid to flow through and both clean and cool the blades 4 and cutters5. The cutters 5 are held in the blades 4 at predetermined angularorientations and radial locations to present a top surface 503 with adesired back rake angle against the formation to be drilled. A fluidchannel 31 is formed in the drill bit body 3, and a plurality of fluidholes 33 communicate with the fluid channel 31. Drilling fluid can bepumped into a space between the blades 4 in selected directions and atselected rates of flow for lubricating and cooling the drill bit, theblades 4, and the cutters 5. The drilling fluid also cleans the bottomof the borehole and removes cuttings as the drill bit rotates andpenetrates the formation.

The drill bit body 3 is substantially cylindrical. The plurality of thecutters 5 are disposed on the outer edge of the blade 4, furthermore,the outer edge of the blade 4 comprises a cone portion 431, a noseportion 432, a shoulder portion 433, and a gauge protection portion 434.The cone portion 431 is close to the central axis of the drill bit body3, the gauge protection portion 434 is located on the side wall of thedrill bit body 3, and the cutters 5 are distributed across the coneportion 431, the nose portion 432, the shoulder portion 433 and thegauge protection portion 434 of the blades 4.

Referring to FIGS. 2A-2C, a typical cutting element (cutter) 5, issubstantially cylindrical having a cutter axis 505, and includes acylindrical bottom portion and a cylindrical top portion. The bottomportion, called a substrate 504, is usually made from hard compositessuch as tungsten carbide, and the top portion, called an ultra-hardlayer 502, is typically made from hard and abrasive material such aspolycrystalline diamond (PCD). The interface 513 between the substrate504 and the ultra-hard layer 502 may be planar or nonplanar, accordingto many varying designs for interfaces known in the art. The substrate504 and the ultra-hard layer 502 are sintered together through a highpressure, high temperature process. On the top end of the ultra-hardlayer 502, a chamfer 507 is machined to increase the durability of thecutting edge while running into the borehole and at the inception ofdrilling, at least along the portion which initially contacts theformation. One skilled in the art will recognize that at least a portionof the chamfer 507 may also function as a working surface that contactsthe subterranean formation during drilling operations. The top surface503 of the ultra-hard layer 502 and the surface of the chamfer 507intersect at a top cutting edge 515. The side wall 512 of the ultra-hardlayer 502 and the surface of the chamfer 507 also intersect at a lowercutting edge 514, which is the main formation cutting edge whosecurvatures are the same as that of the outer cylindrical surface ofsubstrate 504.

For a typical cutter, the top surface 503 of the ultra-hard layer, alsocalled the cutting face, is flat and parallel to the bottom surface ofthe substrate, i.e., perpendicular to the cutter axis 505. The distancefrom any point on the cutting face to the bottom surface of thesubstrate is equal to cutter height 506. It is also noted that thethickness of the ultra-hard layer is uniform if the interface 513 isplanar. A non-planar interface 513 may be employed to reduce the thermalresidual stress at the interface and inside the ultra-hard layer due tothe mismatch of the coefficient of thermal expansion between theultra-hard layer material and the substrate material. In this case, thethickness of the ultra-hard layer is not uniform, but the cutting faceis still parallel to the bottom surface of the substrate andperpendicular to the cutter axis, i.e., the cutting face angle 560between the cutting face and the cutter axis is 90 degrees.

Referring to FIGS. 3A and 3B, the cutter 5 cuts a formation 410 with thetop surface 503. In the drilling process, the drill bit (see FIG. 1)will be positioned at the bottom of a well bore and rotated for cuttingthe inside surface of the cylindrical well bore. Cutters in the bladesare assembled via brazing or mechanical lock at predetermined angularorientations in regard to the formation to be drilled. Drilling fluid ispumped into the inside of the bit body and exits from the nozzles. Asthe drill bit is rotated, the PDC cutters scrape across and shear awaythe underlying earth formation material and withstand great impact fromthe formation.

One feature of the arrangement of the cutter is known as the reliefangle, which is the angle between the cutter axis and the top surface ofthe formation 410. A certain relief angle is necessary to prevent thecutter from rubbing against the formation, avoiding frictional heat andextra reactive torque during drilling.

Another feature of the arrangement of the cutter is known as the backrake angle. The back rake angle is used to describe the working angle ofthe top surface 503. As shown in FIG. 3A, the back rake angle 610 isdefined as the angle between the top surface 503 and a plane normal tothe surface of formation 410 at the cutting edge 514. For a cylindricalflat cutter, the back rake angle 610 is equal to the relief angle 620.The back rake angle 610 in FIG. 3A is greater than the back rake angle612 in FIG. 3B because the relief angle 620 in FIG. 3A is greater thanthe relief angle 630 in FIG. 3B. Desired back rake angle for the mostefficient drilling depends on the type of formation to be drilled.Typically, a drill bit is designed so that the cutter has a relativelylow back rake angle. Low back rake angle provides the drill bit withrelatively high efficiency, by reducing the weight on bit (WOB) requiredto fail a given earth formation, meaning that the rate of penetrationthrough earth formations is high.

However, for hard formations, such as carbonate, igneous rocks andsandstone, a relatively large back rake angle is needed, in order toincrease the strength of the cutting edge and prevent the cutters frombreakage or chipping resulted from the high cutting force acting on thecutters. In this case, the cutting efficiency is reduced and sometimesit is difficult for the cutter to bite into the formation, resulting inunstable drilling.

For soft formations, such as shale, claystone and mudstone, a lowercutting force is required to shear the formation and cutter damage isnot significant. A relatively small back rake angle can be used tomaximize the cutting efficiency without causing cutter damage. However,for the conventional cutter with a flat cutting face, the desired backrake angle might not be achievable. If the back rake angle (same as therelief angle for a planar cutter) is too small, the cutter'scircumferential surface adjacent to the cutting edge will rub againstthe formation or extruded cuttings, increasing the frictional heat andadding extra reactive torque. The increased frictional heat will degradecutter wear resistance and impact resistance and shorten bit life.Another disadvantage of the cutters with a planar cutting face indrilling soft formations, especially shale and claystone under highconfining pressure and high bottom-hole temperature, is the continuousribbon generated during drilling. Continuous ribbons may accumulate andcompact in front of the cutter face and/or between the cutter and therock. Cutting build-up has a major impact on cutter/rock interactions.Energy is lost in plastically deforming the cuttings rather than failingintact rock. Cutting build-up may also lead to other drillingdysfunctions such as poor cooling and even cutter balling. Due to thelarge size of these kinds of cuttings, they could attach to the bladesand the body part of the bit to form balling, such that the work facesof the blades of the bit are clogged, restricting drilling fluid andcutting flow, eventually leading to decrease of mechanical speed, nodrill footage and other issues.

Therefore, it would be advantageous to provide a cutter with reducedback rake angle while maintaining a required relief angle in order toimprove cutting efficiency and service life.

SUMMARY

In one aspect, the present invention is directed to a cutter used on adrill bit for cutting formation. The cutter comprises a substrate, anultra-hard layer, an inclined surface on the top of the ultra-hardlayer, wherein the inclined surface slants downward from a cutting edgeto a trailing edge. In an embodiment, the cutter further comprises achamfer extending from the periphery of the inclined surface to thecutting edge at a side wall of the ultra-hard layer.

In some embodiments pertaining to the inclined surface, the inclinedsurface comprises a cutting ridge extending from the cutting edge to thetrailing edge diametrically on the top of the inclined surface. Two sidesurfaces slant downward respectively from the cutting ridge to theperiphery of the inclined surface. The profile angle at the trailingedge is larger than the profile angle at the cutting edge and the cutterheight at the cutting edge is taller than the cutter height at thetrailing edge. In some embodiments, the cutting ridge is rounded.

In some embodiments pertaining to the inclined surface, the inclinedsurface comprises two cutting ridges intersecting at a cutting point onthe cutting edge and extending from the cutting point outwards at anangle towards the trailing edge. The two cutting ridges separate theinclined surface into two side flat surfaces and a central flat surface.The central flat surface slants downward from the cutting edge to thetrailing edge and the two side flat surfaces slant downward from the twocutting ridges to the periphery of the inclined surface, respectively.The inclined angles of the two side flat surfaces can be equal ordifferent.

In some embodiments pertaining to the inclined surface, the inclinedsurface comprises two converging cutting ridges and one central cuttingridge intersecting at a point away from the cutting edge, and the twoconverging cutting ridges and the central cutting ridge divide theinclined surface into two flat side surfaces and one flat centralsurface. The two flat side surfaces intersect at the central cuttingridge and the two flat side surfaces intersect the central surface atthe two converging cutting ridges, respectively. The outer end of thecentral cutting ridge (close to the cutter periphery) meets the cuttingedge at a cutting point. The central cutting ridge is parallel to thecutter bottom surface of the substrate. The flat central surface issloped. In some embodiments, the central cutting ridge is rounded andforms a second central surface which is curved.

In some embodiments pertaining to the inclined surface, the inclinedsurface comprises two cutting ridges which do not intersect on thecutting surface and extend from the cutting edge at an angle towards thetrailing edge. The two cutting ridges meet the cutting edge and form twocutting points. The two cutting ridges separate the inclined surfaceinto two side flat surfaces and a central flat surface. The central flatsurface slants downward from the cutting edge to the trailing edge andthe two side flat surfaces slant downward from the two cutting ridges tothe periphery of the inclined surface, respectively. The inclined anglesof the two side flat surfaces can be equal or different.

In some embodiments, the ultra-hard layer is formed of PCD and theinclined surface is machined by Electrical Discharge Machining methods.

In another embodiment, the disclosure is directed to a drill bit forcutting formation. The drill bit comprises a bit body, a plurality ofcutters of the present disclosure, and a plurality of blades withpockets to accommodate the cutters, respectively.

The foregoing has outlined rather broadly the features of the presentdisclosure in order that the detailed description that follows may bebetter understood. Additional features and advantages of the disclosurewill be described hereinafter, which form the subject of the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the manner in which the above-recited and otherenhancements and objects of the disclosure are obtained, a moreparticular description of the disclosure briefly described above will berendered by reference to specific embodiments thereof which areillustrated in the appended drawings. Understanding that these drawingsdepict only typical embodiments of the disclosure and are therefore notto be considered limiting of its scope, the disclosure will be describedwith additional specificity and detail through the use of theaccompanying drawings in which:

FIG. 1 is a sectional view of a prior art drill bit;

FIG. 2A is a perspective view of a prior art cutter with planar cuttingface;

FIG. 2B is a sectional view of the cutter in FIG. 2A;

FIG. 2C is a top view of the cutter in FIG. 2A;

FIG. 3A is a schematic illustration of a planar cutter cutting formationwith larger back rake angle;

FIG. 3B is a schematic illustration of a planar cutter cutting formationwith smaller back rake angle;

FIG. 4A is a perspective view of the cutter with nonplanar cutting face,which comprises two inclined side surfaces and one inclined cuttingridge in accordance with one embodiment of the present invention;

FIG. 4B is a front view of the cutter with nonplanar cutting face inFIG. 4A;

FIG. 4C is a sectional view of the cutter with nonplanar cutting face inFIG. 4A;

FIG. 5 is a schematic illustration of the cutter in FIG. 4A cuttingformation with reduced back rake angle;

FIG. 6A is a perspective view of the nonplanar cutter in FIG. 4A with around cutting ridge;

FIG. 6B is a front view of the nonplanar cutter in FIG. 6A;

FIG. 6C is a side view of the nonplanar cutter in FIG. 6A;

FIG. 7A is a perspective view of the cutter with nonplanar cutting face,which comprises three inclined flat surfaces converging at the cuttingedge in accordance with one embodiment of the present invention;

FIG. 7B is a front view of the cutter with nonplanar cutting face inFIG. 7A;

FIG. 7C is a side view of the cutter with nonplanar cutting face in FIG.7A;

FIG. 7D is a top view of the cutter with nonplanar cutting face in FIG.7A with three inclined flat surfaces converging on the cutter peripherybefore the chamfer is constructed;

FIG. 8A is a perspective view of the cutter with three flat surfaces andthree cutting ridges in accordance with one embodiment of the presentinvention;

FIG. 8B is a front view of the cutter with nonplanar cutting face inFIG. 8A;

FIG. 8C is a side view of the cutter with nonplanar cutting face in FIG.8A;

FIG. 9 is a schematic illustration of the cutter in FIG. 8A cutting ahighly heterogeneous formation with interbedded soft and hard sections;

FIG. 10A is a perspective view of the cutter with nonplanar cuttingface, which comprises three inclined flat surfaces which do notintersect at a point on the cutting surface;

FIG. 10B is a front view of the cutter with nonplanar cutting face inFIG. 10A;

FIG. 10C is a side view of the cutter with nonplanar cutting face inFIG. 10A;

FIG. 11A is a perspective view of the nonplanar cutter in FIG. 8A with around central cutting ridge;

FIG. 11B is a front view of the cutter with nonplanar cutting face inFIG. 11A;

FIG. 11C is a side view of the cutter with nonplanar cutting face inFIG. 11A.

DETAILED DESCRIPTION

The particulars shown herein are by way of example and for purposes ofillustrative discussion of the preferred embodiments of the presentdisclosure only and are presented in the cause of providing what isbelieved to be the most useful and readily understood description of theprinciples and conceptual aspects of various embodiments of thedisclosure. In this regard, no attempt is made to show structuraldetails of the disclosure in more detail than is necessary for thefundamental understanding of the disclosure, the description taken withthe drawings making apparent to those skilled in the art how the severalforms of the disclosure may be embodied in practice.

The following definitions and explanations are meant and intended to becontrolling in any future construction unless clearly and unambiguouslymodified in the following examples or when application of the meaningrenders any construction meaningless or essentially meaningless. Incases where the construction of the term would render it meaningless oressentially meaningless, the definition should be taken from Webster'sDictionary 11th Edition.

FIGS. 4A-4C illustrate an embodiment of a cutter 51 of the presentdisclosure. In accordance with the present invention, the cutter 51 hasa substrate 504 and an ultra-hard layer 502 disposed thereon. Theultra-hard layer 502 can be formed of polycrystalline diamond, cubicboron nitride, silicon carbide, and the substrate 504 can be formed oftungsten carbide. The cutter 51 is substantially cylindrical andsymmetrical about a longitudinal cutter axis 505, although such symmetryis not required, and nonsymmetrical cutters are known in the art. Achamfer 507 extends from the periphery of a top surface 503 to a sidewall 512 of the ultra-hard layer 502. Chamfer 507 may extend about theentire periphery of the ultra-hard layer 502 as shown or only a portionto be located adjacent to a cutting edge 521. Although the chamfer 507can increase the durability of the cutting edge, it should be noted thatcutters exhibiting substantially no visible chamber may be employed forcertain applications in selected outer regions of a bit.

The top surface 503 of the cutter in the invention comprises two sidesurfaces 531, 533 which intersect at the center of the cutter and form acutting ridge 541. The top surface 503 can be constructed from a typicalflat cutter by removing materials with a method called loft cut. Thecutting ridge 541 extends downward from the cutting edge 521 to thetrailing edge 523 diametrically on the top surface 503. The two sidesurfaces 531, 533 are slanted downward respectively from the cuttingridge 541 to the periphery of the inclined top surface 503 along theperpendicular direction with respect to the cutting ridge. Theintersection of the cutting ridge 541 and the cutting edge 521, thelowest point on the side surface 531, and the lowest point on the sidesurface 533 define three vertices of a cutting triangle. The projectionof the cutting triangle on a plane perpendicular to the cutting ridge541 will form a cutting triangle profile with three vertices 542, 524,525. Similarly, the intersection of the cutting ridge 541 and trailingedge 523, the lowest point on the side surface 531, and the lowest pointon the side surface 533 define three vertices of a trailing triangle.The trailing triangle projecting onto a plane perpendicular to thecutting ridge 541 will create a trailing triangle profile with threevertices 543, 524, 525.

The vertex 542 of the cutting triangle profile is higher than the vertex543 of the trailing triangle profile. An angle between the lineconnecting vertices 542, 524 and the cutter axis 505 is defined as thefirst cutting edge profile angle 551, and an angle between the lineconnecting vertices 542, 525 and the cutter axis 505 is defined as thesecond cutting edge profile angle 552. An angle between a lineconnecting vertices 543, 524 and the cutter axis 505 is defined as thefirst trailing edge profile angle 555, and an angle between the lineconnecting vertices 543, 525 and the cutter axis 505 is defined as thesecond trailing edge profile angle 556. Using the line connecting thevertices of the triangle profiles as the guide curve, a convex surfacecan be formed. The slopes of the side surfaces are determined by theprofile angles. The profile angles at the trailing edge are larger thanthe profile angles at the cutting edge to keep a reasonable diamondtable thickness at the trailing edge 523. Specially, the first trailingedge profile angle 555 is larger than the first cutting edge profileangle 551, and the second trailing edge profile angle 556 is larger thanthe second cutting edge profile angle 552. The cutting ridge 541 istypically located at the center of the top surface. The profile anglesof each profile may be equal or different. The loft cut is executed byElectrical Discharge Machining (EDM), Laser Ablation, Grinding, or othermaterial reduction methods. It can also be net shaped through sinteringprocess.

By constructing the cutter using the aforementioned methods, the cutterheight 506 at the cutting edge is taller than the cutter height 508 atthe trailing edge. The cutting ridge 541 is declining from the cuttingedge to the trailing edge with an angle 509 larger than 90 degrees. Thecutting ridge inclination is measured between the cutting ridge 541 andthe cutter axis 505.

The advantage of the nonplanar cutter described in FIGS. 4A-4C can beexplained in FIG. 5 and FIG. 3A. FIG. 3A shows a planar cutter cuttingformation with a back rake angle 610 and a relief angle 620. FIG. 5shows a cutter 51 with the inclined cutting face of FIG. 4A cuttingformation with the same relief angle. When cutting into a formation 410,the planar cutter 5 and the non-planar cutter 51 have the same reliefangle 620 in FIGS. 3A and 5. Because of the inclined cutting face, theback rake angle 613 of the cutter 51, which equals to the back rakeangle 610 minus the inclination angle 509 in FIG. 4C plus 90 degrees, issmaller than the back rake angle 610 of the planar cutter 5. The reducedback rake angle and the sharp ridge of the nonplanar cutter in FIGS.4A-4C requires less cutting force to fracture the formation whilemaintaining a reasonable relief angle.

There are some other advantages of the cutter described in FIGS. 4A-4C.The cuttings will remain in contact with the cutting face for a shorterperiod of time with the reduced back rake angle, resulting in lessfrictional heat. The frictional heat will deteriorate the properties ofthe ultra-hard layer such as wear resistance and impact resistance. Thenonplanar cutting face provides a favorable fluid path, allowing thedrilling fluid to cool the cutter more efficiently. The cutting ridge541 and inclined side surfaces 531, 533 will break down the cuttings andreduce the tendency of cutting compaction in front of the cutting ridge,which might lead to other drilling dysfunctions such as poor cooling andeven cutter balling.

In an embodiment of the present disclosure, the inclined cutting surfacemay have a round cutting ridge in the middle. FIGS. 6A-6C illustrate acutter 52 having inclined surface and a round cutting ridge.Specifically, the cutter 52 has a substrate 504 and an ultra-hard layer502 disposed thereon. A chamfer 507 extends from the periphery of thetop surface 503 to the side wall 512 of the ultra-hard layer 502. Thetop surface 503 of the ultra-hard layer 502 is inclined. A cutting ridge541 extends downward from a cutting edge 521 to a trailing edge 523diametrically on the top surface 503. The two side surfaces 531, 533 areslanted downward respectively from the cutting ridge 541 to theperiphery of the inclined top surface 503 along the perpendiculardirection with respect to the cutting ridge 541. At the same time, thetwo side surfaces 531, 533 are slanted downward respectively from thecutting edge 521 to the trailing edge 523.

As will be recognized by those skilled in the art, there are othercutter designs in accordance with the features of this invention. In apreferred embodiment, Referring to FIGS. 7A-7D, a cutter 53 havinginclined surface is illustrated. The cutter 53 has a substrate 504 andan ultra-hard layer 502 disposed thereon. A chamfer 507 extends from theperiphery of a top surface 503 to the side wall 512 of the ultra-hardlayer 502. The top surface 503 of the ultra-hard layer 502 is inclined.

The top surface 503 comprises two inclined flat side surfaces 531 and533 and an inclined flat central surface 532. The central surface 532has an inclination α between the central surface 532 and the bottomsurface of the cutter. The inclination α, in the range of 1-45 degrees,preferred in the range of 3-15 degrees, determines the back rake anglereduction compared to a flat cutter. The side surfaces 531, 533 haveinclinations β and γ with their lower sides intersecting cuttercylindrical surface. The inclinations β and γ are measured between theside surfaces 531, 533 and a cutter axis 505, respectively. The threesurfaces intersect at two cutting ridges 541, 561. Specifically, theflat side surface 531 intersects with the central surface 532 at thecutting ridge 541, and the flat side surface 533 intersects with thecentral surface 532 at the cutting ridge 561. Referring to FIG. 7D, thecutting ridges 541, 561 intersect the cutter periphery at the point 571before the chamfer is constructed and extend from the point 571 to thetrailing edge, such that the two cutting ridges form a substantially “V”type pattern. Referring to FIG. 7A, after the chamfer 507 isconstructed, the cutting ridges 541, 561 intersect the cutting edge 521at the points 572 and 573. The two side surfaces 53 land 533 and thecentral surface 532 slant downward respectively from the cutting edge521 to the trailing edge 523, at the same time, the side surfaces 531,533 slant downward respectively from the two cutting ridges 541, 561 tothe cutter periphery. The side surfaces are symmetric with regard to theplane which passes through point 522 having equal distance to the points572 and 573 and the cutter axis 505 in FIGS. 7A-7B, in which case theinclinations β and γ are equal, but they can be asymmetric in otherembodiments.

FIGS. 8A-8C illustrate an alternative embodiment of a cutter 54 of thepresent disclosure. Similar to the cutter in FIGS. 7A-7D, the cuttingface features three inclined flat surfaces, but they intersect at apoint away from the cutting edge. The cutter 54 has a substrate 504 andan ultra-hard layer 502 disposed thereon. A chamfer 507 extends from theperiphery of the top surface 503 to the side wall 512 of the ultra-hardlayer 502. The central cutting ridge is parallel to the cutter bottomsurface and two diverging cutting ridges extend downward to the cutterperiphery at the trailing edge.

The top surface 503 of the ultra-hard layer 502 is inclined and providedwith three cutting ridges 541, 562 and 563. The inner ends (away fromthe cutter periphery) of the three cutting ridges converge at a point545 on the top surface 503, and the outer ends (close to the cutterperiphery) of the three cutting ridges extend to the outer edge of thetop surface 503. Viewed from the top of the cutter, the three cuttingridges form a substantially “Y” type pattern, and the three cuttingridges divide the top surface into two flat side surfaces 531, 533 andone flat central surface 532. The two flat side surfaces 531, 533intersect at the central cutting ridge 541. The outer end (close to thecutter periphery) of the central cutting ridge 541 meets the cuttingedge 521 at a cutting point. The two flat side surfaces 531, 533intersect the central surface 532 at two diverging cutting ridges 562and 563, respectively. In one embodiment, the central cutting ridge 541is parallel to the cutter bottom surface and two diverging cuttingridges 562, 563 extend downward to the cutter periphery at the trailingedge 523. A slope is measured between the central flat surface and aplane parallel to the cutter bottom surface. In FIG. 8B, the centralsurface 532 has a slope angle S. It is worth mentioning that the centralcutting ridge 541 is parallel to the cutter bottom surface in FIGS.8A-8C, but it can slant downwards from the cutting edge to the centralflat surface with a slope angle which is smaller than the slope angle δof the central surface.

The central ridge cuts the formation and its length can be optimizedbased the depth of cut in highly heterogeneous formation where soft andhard layers are alternating. The embodiment in FIGS. 8A-8C can adapt tothe formation change with a stepped back rake configuration. Referringto FIG. 9, formation 410 is a highly heterogeneous formation with hardand soft layers. When a bit is in a relative hard layer within thehighly heterogeneous formation 410, a larger back rake angle ispreferred to maintain cutter edge strength in preventing breakage orchipping due to high cutting forces acting on the cutters. However, whenthe bit is cutting a relative soft layer within the highly heterogeneousformation, a smaller back rake angle is preferred to improve the cuttingefficiency. Particularly, when cutting into the hard layer of theformation 410, a cutter 54 produces a hard formation ribbon 414 with alow depth of cut 415. In the low depth of cut, the cutting ridge 541contact with the hard formation ribbon, and a back rake angle α is theangle between the cutting ridge 541 and the line 411 normal to thesurface of formation 410. When cutting into the soft layer of theformation 410, the cutter produces a soft formation ribbon 418 with ahigh depth of cut 419. In the high depth of cut, a back rake angle β isthe angle between the central surface 532 and the line 411. Because ofthe slope angle δ of the central surface 532, the back rake angle β issmaller than the back rake angle α, which allows higher rate ofpenetration. Therefore, the cutter of the present invention can adjustthe back rake angle in a heterogeneous formation with the same reliefangle, such that the cutter can improve cutting efficiency and servicelife.

FIGS. 10A-10C illustrate an alternative embodiment of a cutting element55 of the present disclosure. Similar to the cutter in FIGS. 7A-7D andFIGS. 8A-8C, the cutting face features three inclined flat surfaces, butthe three inclined flat surfaces do not interest at a point on thecutting surface.

The cutter 55 has a substrate 504 and an ultra-hard layer 502 disposedthereon. A chamfer 507 extends from the periphery of the top surface 503to the side wall 512 of the ultra-hard layer 502. The top surface 503comprises two inclined flat side surfaces 531, 533 and an inclined flatcentral surface 532. The central surface 532 has an inclination αbetween the central surface 532 and the bottom surface of the cutter.The side surfaces 531, 533 have inclinations β and γ with their lowersides intersecting cutter cylindrical surfaces. The inclinations β and γare measured between the side surfaces 531, 533 and a cutter axis 505,respectively. The three surfaces intersect at two cutting ridges 541,569. Specifically, the flat side surface 531 intersects with the centralsurface 532 at the cutting ridge 541, and the flat side surface 533intersects with the central surface 532 at the cutting ridge 569. Thecutting ridges 541, 569 intersect the cutting edge 521 at points 567 and568 and intersect the trailing edge 523 at points 553 and 554. The twoside surfaces 53 land 533 and central surface 532 slant downwardrespectively from the cutting edge 521 to the trailing edge 523, at thesame time, the side surfaces 531, 533 slant downward respectively fromthe two cutting ridges 541, 569 to the cutter periphery. It is worthmentioning that the side surfaces are symmetric with regard to the planewhich passes through the point having equal distance to the points 567and 568 and the cutter axis 505 in FIGS. 10A-10B, in which case theinclinations β and γ are equal, but they can be asymmetric in otherembodiments. The cutting ridge 541, 569 in the present disclosure aresharp, but they can also be round to improve their impact resistance.FIGS. 11A-11C illustrate an alternative embodiment of a cutting element56 of the present disclosure. Similar to the cutter in FIGS. 8A-8C, butthe central ridge is rounded and forms a curved surface 534 where thegenerating lines 547 are parallel to each other. Specifically, thecutter 56 has a substrate 504 and an ultra-hard layer 502 disposedthereon. A chamfer 507 extends from the periphery of the top surface 503to the side wall 512 of the ultra-hard layer 502. The top surface 503includes a central curved surface 534, a central flat surface 532 andtwo flat side surfaces 531 and 533. The two flat side surfaces 531, 533intersect the central curved surface 534 at the cutting ridges 541 and566 and intersect the central flat surface 532 at the cutting ridges 564and 565. The central curved surface 534 intersects the central flatsurface 532 at the cutting ridge 570 and intersects the side wall 512 ofthe ultra-hard layer 502 at the edge 546, as part of the cutting edge521.

The top surface 503 of the ultra-hard layer 502 is inclined. The centralsurface 532 has a slope angle S. The two side surfaces 531, 533 areslanted downward respectively from the cutting ridges 541 and 566 to theperiphery of the inclined top surface 503 along the perpendiculardirection with respect to the cutting ridges 541 and 566, respectively.At the same time, the two side surfaces 531, 533 are slanted downwardrespectively from the cutting edge 521 to the trailing edge 523. Thegenerating lines 547 of the central curved surface 534 are parallel tothe bottom surface of the cutter or have a sloped angle to the bottomsurface of the cutter (not shown).

For the cutters in FIGS. 7A-7D, FIGS. 8A-8C, FIGS. 10A-10C, and FIGS.11A-11C, the cutting faces are constructed by three flat surfaces exceptthe additional central curved surface in FIGS. 11A-11C. Other shapes ofthe surfaces, such as any convex or concave surfaces, shall also beincluded in the disclosure.

In some embodiments, the present invention also provides a drill bit,which comprises at least one cutter disclosed in this invention in anyposition.

All of the compositions and methods disclosed and claimed herein can bemade and executed without undue experimentation in light of the presentdisclosure. While the compositions and methods of this disclosure havebeen described in terms of preferred embodiments, it will be apparent tothose of skill in the art that variations may be applied to thecompositions and methods and in the steps or in the sequence of steps ofthe methods described herein without departing from the concept, spirit,and scope of the disclosure. More specifically, it will be apparent thatcertain agents which are both chemically related may be substituted forthe agents described herein while the same or similar results would beachieved. All such similar substitutes and modifications apparent tothose skilled in the art are deemed to be within the spirit, scope andconcept of the disclosure as defined by the appended claims.

What is claimed is:
 1. A cutter comprising a substrate; an ultra-hardlayer; an inclined surface on top of the ultra-hard layer; and whereinthe inclined surface slants downward from a cutting edge to a trailingedge.
 2. The cutter of claim 1, further comprising a chamfer extendingfrom a periphery of the inclined surface to the cutting edge at a sidewall of the ultra-hard layer.
 3. The cutter of claim 1, wherein theinclined surface comprises a cutting ridge extending from the cuttingedge to the trailing edge diametrically on top of the inclined surfaceand two side surfaces slanting downward respectively from the cuttingridge to a periphery of the inclined surface.
 4. The cutter of claim 3,wherein a profile angle at the trailing edge is larger than a profileangle at the cutting edge.
 5. The cutter of claim 3, wherein the cuttingridge is a round cutting ridge.
 6. The cutter of claim 1, wherein thecutter height at the cutting edge is taller than the cutter height atthe trailing edge.
 7. The cutter of claim 1, wherein the inclinedsurface comprises two cutting ridges intersecting at a cutting point onthe cutting edge and extending from the cutting point to the trailingedge.
 8. The cutter of claim 7, wherein the two cutting ridges separatethe inclined surface into two side flat surfaces and a central flatsurface; wherein the two side flat surfaces slant downward from the twocutting ridges to a periphery of the inclined surface; and wherein thecentral flat surface slants downward from the cutting edge to thetrailing edge.
 9. The cutter of claim 7, wherein the two cutting ridgesseparate the inclined surface into concave or convex surfaces.
 10. Thecutter of claim 1, wherein the inclined surface comprises two convergingridges and a central cutting ridge intersecting at a point away from thecutting edge, and the two converging ridges and the central cuttingridge divide the inclined surface into two side surfaces and one centralsurface.
 11. The cutter of claim 10, wherein the two side surfaces areflat and the one central surface is flat.
 12. The cutter of claim 10,wherein the two side surfaces intersect at the central cutting ridge andthe two side surfaces intersect the central surface at the twoconverging ridges.
 13. The cutter of claim 10, wherein the two cuttingridges separate the inclined surface into concave or convex surfaces.14. The cutter of claim 10, wherein an outer end of the central cuttingridge meets the cutting edge at a cutting point; wherein the centralcutting ridge is parallel to a cutter bottom surface of the substrate;and wherein the central surface has an inclination toward the trailingedge.
 15. The cutter of claim 10, wherein the central cutting ridge is around cutting ridge and forms a curved central surface; and whereingenerating lines of the curved central surface are parallel to a bottomsurface of the cutter or have a sloped angle to the bottom surface ofthe cutter.
 16. The cutter of claim 15, wherein the curved centralsurface can be a concave or convex surface.
 17. The cutter of claim 1,wherein the inclined surface comprises two cutting ridges which do notintersect at a point on a cutting surface and extend from a cuttingpoint to the trailing edge.
 18. The cutter of claim 17, wherein the twocutting ridges separate the inclined surface into two side flat surfacesand a central flat surface.
 19. The cutter of claim 17, wherein the twocutting ridges are round; wherein a central flat surface slants downwardfrom the cutting edge to the trailing edge; and wherein two side flatsurfaces slant downward from the two cutting ridges to a periphery ofthe inclined surface.
 20. The cutter of claim 17, wherein the twocutting ridges separate the inclined surface into concave or convexsurfaces.
 21. The cutter of claim 1, wherein the ultra-hard layer isformed of polycrystalline diamond.
 22. The cutter of claim 1, whereinthe inclined surface is loft cut by electrical discharge machining, bylaser processing, by grinding, by other material reduction methods, ornet shaping from a sintering process.
 23. A drill bit comprising atleast one cutter of claim 1.